Commitments and Contingencies (Details Textual) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013 Number	Sep. 30, 2012	Sep. 30, 2013 Number	Sep. 30, 2012	Dec. 31, 2012
Commitments and Contingencies (Textual) [Abstract]
Number of outstanding letters of credit	6		6
Letter of credit obligation	$ 5,658,000		$ 5,658,000
Outstanding construction financings for leased properties	158,006,000		158,006,000		162,984,000
Additional financing to complete construction	261,625,000		261,625,000
Total contingent purchase obligations	59,561,000		59,561,000
Minimum part of economic life of the leased asset to be classified as capital lease			75.00%
Minimum net present value of the future minimum lease payments to be classified as capital lease.	90.00%		90.00%
Operating lease obligations relating to certain ground leases	882,088,000		882,088,000
Rental expense related to company office space	410,000	330,000	1,217,000	931,000
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals	44,987,000		44,987,000
Capital Leases, Future Minimum Payments Due	$ 118,463,000		$ 118,463,000